As an intermediate raw material or the like in the chemical industry, phosphonates having an alcoholic hydroxyl group have various applications. For example, as an intermediate in synthesis for preparing phosphoric esters that are known generally as a flame-retarder for resins, the phosphonates are used for preparing the phosphoric esters by being reacted with a compound having a P—Cl bond.
As a process for preparing such phosphonates, various processes are known.
For example, Japanese Unexamined Patent Publication No. Sho 49 (1974)-126623 describes a process for synthesizing phosphonates having an alcoholic hydroxyl group by reacting a dialkyl phosphite with a carbonyl compound in the presence of a catalyst of an amine compound such as triethylamine or tributylamine and a metal alkoxide such as sodium ethoxide.
With this process, however, the target compound cannot be obtained in a high yield, and unreacted raw materials are left in the reaction product. Further, improving the purity of the target compound requires a step for removing the unreacted raw materials, which leads to a reduced yield and an increased amount of a by-product due to thermal history applied at the removal step.
Also, the specification of British Patent No. 682706 describes a process for synthesizing phosphonates having an alcoholic hydroxyl group by reacting a dialkyl phosphite with a carbonyl compound in the presence of a catalyst of an alkali metal such as metallic potassium or metallic sodium.
The alkali metal used in this process as the catalyst, however, poses a danger in handling during storage or use, and therefore the use of the alkali metal is not preferable in industry. Further, the yields of the target compounds mentioned in the Examples of this patent document are not satisfactory.
Generally, if carbonyl compounds used as a raw material are an aldehyde or a ketone having a sterically bulky substituent, the carbonyl compounds are prone to be inferior in reactivity. For this reason, there has been a demand for development of a process for preparing phosphonates in a high yield even with the use of such a carbonyl compound having a sterically bulky substituent as a raw material.